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return value of subroutines and SCXT

Otto Salvatore

Hi,

i am wondering how to give back a value of a subroutine to the calling routine and use a register when using scxt.

example:

SCXT CP,#0FC40h

NOP

CALLS something

CMP R10, ONES

JMP CC_NE, somewhere

POP CP

NOP

the problem is i would like to pop cp direktly afer the subroutine returns, but in this case R10 is lost.

Parents
  • 0

    You can access the registers of any register bank as internal RAM locations. In your example register R10 of the bank at 0FC40H is the RAM word at address 0FC54. Of course you are then limited to the commands supporting direct memory word access. You would have to change the command:

    CMP   R10,ONES


    to

    CMP   0FC54H,ONES

    However, it would be better to use symbolic names for the register banks:

    ?C_MAINREGISTERS  REGDEF  R0 - R15   ;the default register bank (see START167.ASM)
ALT_REGS          REGDEF  R0 - R15   ;your alternate register bank

;Alternate bank RAM addresses
ALT_R0    EQU   (ALT_REGS+0)
ALT_R1    EQU   (ALT_REGS+2)
.
ALT_R10   EQU   (ALT_REGS+20)
.
ALT_R15   EQU   (ALT_REGS+30)

    Now you could write:

    CMP  DPP3:ALT_R10,ONES

    The advantage in this approach is that you don't need to worry where in RAM the registers are actually located.

    I doubt that you don't really need all 16 registers in the alternate register bank. If this is true, you could only allocate as many registers as you actually need (see the REGDEF documentation).

    Sauli

    P.S. Don't ask me what the difference between REGDEF and REGBANK is - I don't know.

Reply
  • 0

    You can access the registers of any register bank as internal RAM locations. In your example register R10 of the bank at 0FC40H is the RAM word at address 0FC54. Of course you are then limited to the commands supporting direct memory word access. You would have to change the command:

    CMP   R10,ONES


    to

    CMP   0FC54H,ONES

    However, it would be better to use symbolic names for the register banks:

    ?C_MAINREGISTERS  REGDEF  R0 - R15   ;the default register bank (see START167.ASM)
ALT_REGS          REGDEF  R0 - R15   ;your alternate register bank

;Alternate bank RAM addresses
ALT_R0    EQU   (ALT_REGS+0)
ALT_R1    EQU   (ALT_REGS+2)
.
ALT_R10   EQU   (ALT_REGS+20)
.
ALT_R15   EQU   (ALT_REGS+30)

    Now you could write:

    CMP  DPP3:ALT_R10,ONES

    The advantage in this approach is that you don't need to worry where in RAM the registers are actually located.

    I doubt that you don't really need all 16 registers in the alternate register bank. If this is true, you could only allocate as many registers as you actually need (see the REGDEF documentation).

    Sauli

    P.S. Don't ask me what the difference between REGDEF and REGBANK is - I don't know.

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